RODENTIA 



447 



in some other species, as in 

 Beaver, glandular masses are 



stomach is much dilated, forming a large egg-shaped sac with 

 thickened glandular walls ; and 

 Lophiomys imhausi and in the 

 attached to and open into the 

 cardiac or pyloric pouches. The 

 alimentary canal (Fig. 196) of 

 all Rodents, with the exception 

 of the Dormice (Myoxidce), has 

 a caecum, which is often of great 

 length and sacculated, as in the 

 Hares, Water- Voles, and Porcu- 

 pines. In some instances, as in 

 the Hamster and Water-Vole, 

 the long colon is spirally twisted 

 upon itself near its commence- 

 ment. The liver is typically 

 divided in all, but the lobes are 

 variously subdivided in the 

 different species (in Capromys 

 they are divided into minute 

 lobules) ; and the gall-bladder, 

 though present in most, is absent 

 in a few. In most species the 



Fio. 196. Alimentary canal of Rat (Mus decu- 



penis (which is generally pro- a '"' s) ' th f ! f ater , >? rt f the T" i! : testine 



.-,.. i i being omitted, o, (Esophagus ; d, duodenum ; 



vided with a bone) can be more i t n eum cm, csecum ; c, colon. 

 or less completely retracted 



within the fold of integument surrounding the anus, where it lies 

 curved backwards upon itself under cover of the integument. It 

 may, however, be carried forward some distance in front of 

 the anal orifice, from which in the breeding season, as in the 

 Voles and Marmots, the prominent testicular mass separates it. 

 The testes in the rutting season form projections in the groins, 

 but (except in the Duplicidentata) do not completely leave the 

 cavity of the abdomen. Prostatic glands and, except in the 

 Duplicidentata, vesiculae seminales are present in all. The uterus 

 may be double, each division opening by a separate aperture into 

 a common vagina, as in Leporidce, Sciuridce, and Hydrochoerus, or 

 completely two-horned, as in most species. The mammae vary in 

 number and position from the single abdominal pair of the Guinea- 

 Pig to the ten thoracico- abdominal pairs found in some of the 

 Rats. In the Ododontidce the mammae are placed high up on the 

 sides of the body. 



The peculiar odour evolved by many Rodents is due to the 

 secretions of special glands, which may open either into the 

 prepuce, as in Mus, Arvicola, Cricetus, etc., or into the rectum, as in 

 Arctomys and Aulacodus, or into the passage common to both, as in 



